1. Field of the Invention
The present invention is directed to a method for manufacturing a pulse generator that acts on the basis of sudden reversal of the magnetic poles given an applied magnetic field, of the type wherein the pulse generator is formed by an elongated composite member of at least two materials that have different thermal expansion behavior and are mechanically braced relative to one another by means of a thermal treatment.
2. Description of the Prior Art
German Patent 31 52 008 discloses a pulse generator formed by a composite member operating as described above. This composite member contains a core and a jacket or envelope whose materials can partially or completely consist of magnetic materials having different coercive field strengths. Given the employment of two magnetic materials with different coercive field strength, an alloy in the range, for example, of 45 through 55% cobalt by weight, 30 through 50% iron by weight and 4 through 14% chromium plus vanadium by weight is employed for the magnetically harder material, whereas nickel is provided as the soft-magnetic material. A defined tension state is produced with a thermal treatment in this known pulse generator by incorporating a material constituent having shape memory or by employing materials having different coefficients of thermal expansion, this tension state yielding a sudden reversal of the magnetic poles in the stressed, soft-magnetic constituent of the composite member, in the presence of the influence of an external magnetic field.
This known composite member exists as an elongated magnetic switch core.
German Published Application 29 33 337 discloses the use of a composite member composed of nickel or unalloyed steel as a bracing or stressing constituent and the use of a cobalt--vanadium--iron alloy as a magnetically active switch component. A thermal treatment is implemented in the manufacture of this known component. First, the wire, which preferably constitutes the composite member, is heated to such an extent that one material constituent plastically deforms under the arising stresses, so that these stresses are largely dismantled. During subsequent cooling, the different coefficients of thermal expansion in turn cause mechanical stresses to arise that, due to the lower temperature, no longer lead to a plastic deformation and, due to the magnetostriction of the magnetically active constituent, lead to the sudden reversal of the magnetic poles in the magnetically active constituent when a specific magnetic field is applied.
An elongated composite member having a low response field strength of 1.0 Oe (approximately 0.8 A/cm) is disclosed in U.S. Pat. No. 4,660,025. For example, an elongated wire of amorphous material that is 7.6 cm long is disclosed therein and it is recited that the length of this wire can be between 2.5 and 10 cm. The internal stresses derived by quenching the material in the production of the amorphous state are the cause of the magnetic skip behavior.
German OS 34 11 049 employs a combination of hard-magnetic and soft-magnetic alloys for manufacturing the composite member. From aforementioned German Patent 31 52 008 it is known that the hard-magnetic constituent can simultaneously serve the purpose of stressing the soft-magnetic constituent. This structure has the advantage that a wire having a high-strength cladding is obtained and that relatively short wires can be provided.
The magnetization characteristic shifts due to the magnetization of the hard-magnetic cladding of a composite member, so that demagnetization zones at the edge of the strip are largely avoided due to the flux in the hard-magnetic cladding, resulting in a skip-like reversal of the magnetic poles (Barkhausen skip), given the reversal of the magnetic poles in one direction, whereas this Barkhausen skip is absent given a reversal of the magnetic poles in the other direction. Significantly shorter switch cores can be employed, since the permanent magnet largely prevents demagnetization zones at the ends of the wire (pulse generator).